Cushiony packaging

ABSTRACT

A paper sealing tape in which the paper is from about 40 to about 90 pound weight, one face of the paper has a slip coating, and the other face carries a layer of pressure-sensitive cement in which is embedded reinforcing fibers to give the tape a breaking strength about 100 or more pounds per two inch width.

The present application is in part a continuation of Ser. No. 82,794filed Aug. 6, 1987, which in turn is a continuation-in part of SerialNos.

Ser. No. 783,430 filed Oct. 4, 1985 (U.S. Pat. No. 4,693,056)

Ser. No. 873,819 filed Jun. 13, 1986 (subsequently abandoned)

Ser. No. 940,566 filed Dec. 12, 1986 (U.S. Pat. No. 4,698,254) and

Ser. No. 142,075 filed Jan. 11, 1988 (now abandoned).

The present invention relates to wrapping and packaging materials.

Among the objects of the present invention is the provision of improvedarticles useful for packaging and wrapping.

The foregoing as well as still further objects of the present inventionwill be more fully understood from the following description of severalof its embodiments, reference being made to the accompanying drawings,in which:

FIG. 1 is a sectional view of a packaging laminate according to thepresent invention;

FIGS. 2 and 3 are sectional views of sealing tapes that can be used toseal packages pursuant to the present invention; and

FIGS. 4, 5 and 6 are isometric views of packaging envelopesrepresentative of the present invention.

Where articles are to be packaged in foam-lined wrappers, as in theparent applications, corrugated paperboard and open-faced corrugatedpaperboard make very effective supports for the foam. The open-facedmaterial is particularly desirable, as shown in application Ser. No.938,600 filed Dec. 5, 1986 and subsequently abandoned, inasmuch as theopen-face construction makes it possible to feed that material from acoiled-up roll. The foam can be applied to the open face or to theclosed face of the open-face board.

A sandwich of cross-tensilized polyethylene films with an overallthickness of up to about 1/5 millimeter also makes a very good foamsupport. Where the foam is applied in stripes of thermoplastic resin,two stripe-carrying sheets of paper, or portions of one such sheet, canbe heat sealed together quite readily and effectively foam-to-foam. Suchheat sealing is also effective when the foam stripes carry or are coatedwith an antistat agent or a volatile corrosion inhibitor, or both, alsoas described in the parent applications.

The stripe-carrying sheets can also be adhered to each other withoutheating, by use of top coatings of cohesive-nonadhesive cements asdescribed in the parent applications, or of pressure-sensitive cements.The cushiony character of the foam stripes permits the stripes to becompressed somewhat to obtain greater contact between the sheet portionsto be thus cemented together. However, the simple application of acohesive-nonadhesive top coating will cause more of such coating tobuild up between foam stripes as compared to on top of foam stripes, andthis further improves the cementing.

The following foam-forming formulations are suitable for use in applyingthe stripes and in applying continuous foam coatings:

EXAMPLE 1

    ______________________________________                                        Natural rubber latex (62% solids)                                                                   100 g.                                                  Ammonium stearate (33% in water)                                                                    2 g.                                                    Acrylic thickener     3.5 g.                                                  Commercial curing mixture                                                                           13 g.                                                   ______________________________________                                    

One effective curing mixture is a mixture of, by weight:

    ______________________________________                                        Powdered sulfur         1.65 parts                                            Powdered zinc oxide     1.25 parts                                            Zinc diethyl dithiocarbamate                                                                          1.00 part                                             Zinc-2-mercapto-benzothiazole                                                                         1.25 parts                                            Phenolic antioxidant    0.75 part                                             ______________________________________                                    

The ingredients are carefully added to the latex to keep fromdestabilizing it, and the entire mixture stirred slowly at first for thesame reason. When the mixing is complete, the mixture is then foamed bybeating air into it with a household beater. This takes several minutesto provide a low-density microfoam that has an expansion of about 3 andshows very little flow, but is readily spreadable. Transferring it to afeed trough and moving a support sheet of 30-pound Kraft paper throughat about 30 centimeters per second with slots about one centimeter wideand about three millimeters deep, followed by baking at about 170° C.for about one minute, produces a very desirable cushiony product. Thecured foam stripes in this product are about one millimeter wider thanthe slots. The same results are obtained with a hand-held spreader barwhich is pushed through a layer of the microfoam, without the help ofthe foregoing apparatus.

Synthetic SBR rubber latex can be substituted for the natural rubberlatex, and the antioxidant can be omitted if the cushioned sheets are tobe used right away. The thickener can also be omitted, in which eventthe liquid content of the microfoam is preferably reduced as by use ofmore concentrated latex and additives, and by subjecting the uncuredmicrofoam to curing heat before or as it is pushed through the spreaderslots. The resulting cured product may have its foam stripes about 2 to4 millimeters wider than the slots.

Other thickeners, such as cellulose ethers, can be used in place of orin addition to some or all of the acrylic thickeners.

Other resins such as polyvinyl chloride or polystyrene or polyurethanescan be used in place of or in addition to the rubber in the latex.Foaming can be effected by incorporating a gas-generating foaming agentin with the resin, rather than or in combination with the beatingaction. This is shown in U.S. Pat. No. 4,636,425 as well as in thefollowing example:

EXAMPLE 2

A polyethylene foam mixture is prepared according to Japanese PatentApplication No. 41-23660, published Aug. 22, 1970 under Number 45-25398.This mixture consists of, by weight:

    ______________________________________                                        Polyethylene powder                                                                              400 parts                                                  Sodium silicate (Na.sub.2 SiO.sub.3)                                                             31 parts                                                   Silica gel (SiO.sub.2)                                                                           51 parts                                                   Water              18 parts                                                   Hydrated alumina    5 parts                                                   ______________________________________                                    

This mixture is heated to about 150° C. to melt the polyethylene andfoam it up. While hot, it is passed through the slots of the spreaderbar.

The cushiony foam-carrying sheets of the present invention can be coatedwith cohesive-nonadhesive or antistat agents or volatile corrosioninhibitors or any combination of two or three, as described in theparent applications. Particularly desirable antistat-containingformulations are:

EXAMPLE 3

The following materials are mixed in the described order given in partsby weight:

    ______________________________________                                        Natural rubber latex (62% solids)                                                                     100.0                                                 Colloidal silica in mineral oil (defoamer)                                                            .2                                                    Water                   23.6                                                  KOH Solution (45) solids) in water                                                                    1.1                                                   Nonionic surfactant     .3                                                    Acrylic thickener       1.3                                                   Water                   18.0                                                  Phenolic antioxidant (50% in Toluene)                                                                 2.1                                                   Acrylic thickener       1.7                                                   Water                   16.7                                                  Sorbitol solution (70% solids) in water                                                               3.5                                                   Attapulgite clay        22.4                                                  ______________________________________                                    

Just before applying, add the following blend:

    ______________________________________                                        Polyethylene glycol (400 molecular weight)                                                             7.1                                                  Polyvinylpyrrolidone     .7                                                   KOH (flake)              .1                                                   ______________________________________                                    

This composition is preferably applied by roll coating so as to form acoating which after drying weighs about 14 to about 22 grams per squaremeter. It can also be sprayed on, in which event the thickener andsurfactant are not needed. The dried coating is an effectivecohesive-nonadhesive layer, and the omission of the sorbitol onlyslightly reduces its effectiveness. Omitting the clay increases itsaggressiveness. The polyvinylpyrrolidone increases its stability.Additional antioxidant can be added to lengthen the shelf life of thedried coating.

EXAMPLE 4

The following volatile corrosion inhibitor coating, in parts by weight,can be used by itself or as an undercoating over which an antistatcoating such as that of Example 3 can be applied.

    ______________________________________                                        Adhesive-type ethylene-vinylacetate                                                                   100.0                                                 copolymer emulsion (55% solids) in water                                      Water                   39.0                                                  2-amino-2-ethyl-propanediol-1,3                                                                       30.0                                                  Dicyclohexylamine       30.0                                                  Benzotriazole (35% in polypropylene                                                                    5.0                                                  glycol having a molecular weight of 400)                                      Nonionic surfactant      .1                                                   ______________________________________                                    

Coating weights, after drying, are preferably from about 14 to about 22grams per square meter.

The Example 4 coating can, if desired, also containcohesive-nonadhesive, as described in the parent applications, Moreover,cohesive-nonadhesive coatings can contain microcapsuled volatilecorrosion inhibitors or perfume or insecticide or the like. Suchmicrocapsules are described in U.S. Pat. No. 4,643,764 and in the priorart of record in that patent and are commercially available. Whenincorporated in an amount of 2% to 5% by weight into thecohesive-nonadhesive will not significantly detract from itscohesiveness.

When a laminate containing such microcapsules is part of a wrapper andis unwrapped, some of the microcapsules rupture, releasing perfume orother ingredients. When used to wrap corrodible metals, handling of awrapped package will also cause such rupture to release volatilecorrosion inhibitor, for example. A strip of such a microencapsulatedinsecticide-containing sheet can also be used as an animal collar torelease insecticide and/or insect repellent whenever rubbed and so helpkeep insects from bothering the animal.

The microcapsule-containing coating can be applied over a backing sheetsuch as paper or to the paper or foam face of a paper-foam laminate.Such paper or laminates can be manufactured in long lengths with linesof perforations to make it easier to tear off short lengths and/orwidths for any desired use.

These formulations are also very effective when coated on a laminate ofordinary microfoam sheeting about 11/2 millimeters thick, laminated to1/40 millimeter thick polyethylene terephthalate film aluminized on oneor both faces. This is illustrated in FIG. 2 where 31 is thepolyethylene terephthalate, 33 and 35 are its metallized faces, 37 isthe microfoam sheet, and 39 is the cohesive-nonadhesive coating.

Rubber foams, as in Example 1, are particularly desirable when that foamis to be coated with rubber-based cohesive-nonadhesive. Thus, apackaging wrapper laminate of paper or open-faced paperboard laminatedto rubber foam sheeting or to rubber foam stripes, coated with arubber-based cohesive-nonadhesive as described in the parentapplications, provides an exceedingly strong cohesive bond when foldedinto foam-to-foam contact or when pressed into such contact with anothersuch wrapper. In addition, the shelf life of such coated wrappers islonger than that of wrappers in which the foam is not rubber-based.These improvements are due to the chemical identity between the foampolymer and the cohesive-nonadhesive polymer.

It is frequently desirable to use gummed tape to seal packages or toapply to the outside of book bindings, or the like. To this end, it isdesirable to have a strong tape, yet an inexpensive one, that does notcontain resin film and does not use re-moistening adhesive. This isshown in FIG. 2 which illustrates such tape 20 on an enlarged scale aswell as the manner in which it is manufactured. The tape is essentiallya pressure-sensitive paper tape having a sheet of paper 22 with one facecarrying a layer 24 that does not permit bonding to pressure-sensitivecement for example. Such release papers in which layer 24 is an acrylicrelease coat of Rhoplex R-225 for example, are readily availablecommercial products.

The opposing face 36 of sheet 22 is coated with a reinforcement layer 38of open-weave glass fibers 30 embedded in a pressure-sensitive cement32. One particularly desirable technique for applying such reenforcinglayer is also illustrated in FIG. 2. An inexpensive release sheet 34such as siliconized paper is first coated with a layer of hot meltpressure-sensitive cement in which is embedded reenforcing filaments,which layer corresponds to 38. A rubber-based pressure-sensitive cementis suitable, as is a diamond-pattern woven glass fiber reenforcement inwhich the fibers are four mils thick and the diamonds about 5 mm. by 5mm.

The thus coated release sheet 34 is now rolled against the paper sheet82 to cause the pressure-sensitive cement 88 to transfer to the face 36of the paper sheet. The resulting laminate makes a very effectivere-enforced sealing tape after pulling off release sheet 34. By slicingthe laminate down to two inches or so in width, the resulting narrowtape can be easily used to seal packages made of corrugated paperboardor punched out pieces of such board, or the like. It is very strong yetinexpensive, and it is free of coherent resin film so that it does notcomplicate the recycling of the packaging. In addition, it does notrequire moistening so that a sealing operation is very simple to carryout.

Because of the release nature of coating 24, the laminate can be rolledup and unrolled, after sheet 34 is removed, without having thepressure-sensitive layer adhere to the backs of the roll turns. The tapeis accordingly very simply used without the complication that would becaused by the presence of sheet 34.

Sheet 22 of 57 pound natural Kraft is strong enough, when reenforced asindicated, for general tape applications, but stronger or weaker papersfrom about 40 pound to 90 pound can be used. The reenforcement should besuch as to bring the breaking strength of the tape to at least about 100pounds per two inch width, and can use fibers such as nylon in place ofthe glass.

The reenforcing pattern can be varied, and the fibers can even bewithout a fixed pattern, as by laterally pressing a cylindrical looselywound roll of the fibers against the cement 32, or by dropping a streamof loosely cut fibers on the cement.

Sheet 34 can be reused after it is removed from the complete laminate,by recoating it and then using to prepare additional laminate. Therelease coatings can also be varied to suit circumstances.

Sheet 43 carries the moistenable gum layer 45, a layer which in theinterest of economy, can be a simple cooked starch dextrin. Such acoating when dry or wet will not adhere to the tensilized polyethylene,even if that polyethylene is corona treated.

The crossed polyethylene layers 41 contribute considerable tensilestrength as well as abrasion resistance to the tape, even when the totalthickness of those polyethylene layers is as small as 1.20 millimeter.Thicknesses over about 0.08 millimeter are not helpful.

Again, in the interest of economy, sheet 43 is as thin asconvenient--generally not over 1/20 millimeter thick. It can bepre-coated with the gum layer 45 before being laminated to thepolyethylene base 41, or it can be top coated after such lamination.

In place of the gum 45, a pressure-sensitive adhesive such as those ofSer. No. 768,103 filed Aug. 21, 1985, now abandoned, can be adhereddirectly to the cross-tensilized polyethylene backing 41, whether or notthe polyethylene surface is corona treated, and without the use of papersheet 43 or any other intervening sheet. However, such a tape is moreexpensive to manufacture and needs special attention, such as a coveringslip sheet, to keep the pressure-sensitive coating from prematurelyadhering to objects which it may contact before it is used.

The very strong support provided by the cross-tensilized polyethylenecombination 41 can also be used to support a layer of cushiony foamadhered to the polyethylene through an intervening paper layer in thesame manner as in FIG. 3. The exposed foam surface of such a combinationcan then carry a cohesive-nonadhesive coating and/or an antistat, and/ora volatile corrosion inhibitor, and is a desirable protective wrappingwhen the foam layer is from about 1/16 millimeter to about threemillimeters thick. Here again, the paper layer can be omitted as byusing a pressure-sensitive adhesive to laminate the foam directly to thepolyethylene.

The wrapper sheets of FIGS. 1 and 2 are desirably used by first formingthem into envelopes or pouches, although they can alternatively be usedto make packaging sandwiches as described in the parent applications.FIG. 4 shows an envelope 50 made from a laminate of metallizedpolyethylene terephthalate laminated to a sheet of foam as illustratedin FIG. 2. Two such laminates 52 and 54 are superimposed with the foamlayer 56 of sheet 52 engaging foam layer 58 of sheet 54. Thissuperimposed combination then has three of its edges 61, 62 and 63 heatsealed to adhere the sheet edges together. Such heat sealing can be bythe techniques described in the parent applications or as in U.S. Pat.No. 4,603,540 by use of heated narrow wheels or discs which areyieldably held edge to edge with the superimposed sheet edges passedbetween the heated wheel edges so those heated edges engage themetallized polyethylene terephthalate coverings 66 and 68. Because thesecoverings are as thin as 1/40 millimeter or less, heat from the heatedwheel edges readily penetrates through to the foam and heat seals thefoam edges together. The heated wheel edges need only be about one totwo millimeters wide, the wider edges being suitable for heat sealingalong the center line of a wide sandwich of wrapping sheets which canthen be cut along the center line of the heat seal to provide twoseparate heat-sealed edges. Such wider wheel edges can also be fittedwith cutting blades centrally located around their rims, so they cutthrough the sandwich as they heat seal.

Another very effective heat-sealing technique uses an elongated narrowmetal bar which can have a knife edge and be heated by an electriccurrent that is passed through it, as in U.S. Pat. No. 4,630,429. Afterit is heated, it is pushed through the aligned wrapper sheets to beheat-sealed together. This is particularly effective when thefoam-backing layer is thermoplastic and thus readily cut through by thehot bar. The bar can be fitted between gripping jaws that secure thealigned wrapper sheets on both sides of the bar and hold them in placeduring the bar-pushing step. The advancing edge of the hot bar need onlybe about one to two millimeters wide.

Similar heating can be applied to a cutting bar or knife used to cutthrough a cold-sealed combination of resin-carrying sheets. Thus, asdescribed in Ser. No. 783,430, filed Oct. 4, 1985, now U.S. Pat. No.4,693,056 automatic or semi-automatic packaging of relatively smallarticles can be effected in an elongated sandwich of overlyingfoam-paper laminates that are fed into foam-to-foam engagement through asealing apparatus that presses against the side edges of the sandwich.Adhesive or cohesive-nonadhesive coatings on the foam faces are in thisway, without the need for heating, cohered to each other around asuccession of the individual articles. The elongated assembly is thentransversely cut into individual packages by a transversely extendingpressing bar and knife combination. Heating that knife to a temperaturenot high enough to melt the foam helps keep down the accumulation ofresin on the knife.

The transverse knife preferably has a serrated cutting edge and can alsobe heated for similarly making transverse cuts on a folded-overfoam-paper laminate for which no side edge sealing is needed, as whenpreparing a succession of envelope-type packages. If desired, thefolded-over packaging can also be effected with one side edge seal thatseals the envelopes.

The envelope of FIG. 4 preferably has an antistat coated on orincorporated into the foam layers 56 and 58 to prevent buildup of staticelectricity when sensitive electronic articles are slipped into orwithdrawn from the envelope. Where those articles are also corrodible,the foam preferably also carries a volatile corrosion inhibitor such asthose of the parent applications.

While volatile corrosion inhibitors can be mixed with antistats to makean effective coating formulation, they can be applied in separatelayers, in which event the volatile corrosion inhibitor layer is appliedfirst and covered with the antistat layer, as described above inconnection with Example 4. An example of a single coating formulationis:

EXAMPLE 5

In parts by weight:

    ______________________________________                                        Adhesive ethylene-vinyl Acetate                                                                        100.0                                                copolymer emulsion (55% solids) in water                                      Water                    39.0                                                 2-amino-2-ethyl-propanediol-1,3                                                                        30.0                                                 Dicyclohexylamine        30.0                                                 Benzotriazole (35% in Xylene)                                                                           5.0                                                 Nonionic surfactant       .1                                                  Polyethylene glycol (400 molecular weight)                                                              3.6                                                 Polyvinyl pyrrolidone     .4                                                  KOH (flake)               .1                                                  ______________________________________                                    

The envelope of FIG. 4 has a flap 70 that projects from one of thesheets 54. When the envelope is used, this flap is preferably foldedover the outer face of sheet 52 and can be adhered to that sheet as bystapling or by adhesive such as the cohesive-nonadhesive applied to theinner face of the flap and to the outer portion of sheet 52 engaged bythe flap when it is folded over. Gummed tape such as the tape of FIG. 3can also be used to hold the flap in place. Alternatively the flap canbe yieldably held by a heat-seal line near its bight, as in FIG. No. 2of application Ser. No. 200,671 filed May 31, 1988, now U.S. Pat. No.4,987,997.

The envelope of FIG. 4 can be made from a single sheet of laminate thatis folded at the location of edge 63 to provide the illustratedconfiguration but requiring only two side sealings, at 61 and 62. A pairof grooved plastic mating strips that interlock can be used instead of aflap, as by heat sealing one mating strip to the inside surface of onewall of the envelope, and the other to the inside surface of theopposite wall.

Polyethylene foam from 1/16 to three millimeters thick makes a verysuitable cushiony layer when supported on a polyethylene terephthalatefilm 1/40 millimeter thick metallized on one or both faces. Such foamcan be manufactured with an antistat agent incorporated in it asdescribed in U.S. Pat. No. 4,618,630, and even when not corona-treatedwill laminate to the polyethylene terephthalate with pressure-sensitiveadhesive. The exposed foam face of that laminate can be coated with moreantistat agent, or with volatile corrosion inhibitor or withcohesive-nonadhesive, or with combinations of two or all three of them.

Where a laminate has an exposed aluminized surface on polyethyleneterephthalate and is to be wound up with that aluminized surface incontact with material having some tack, such as a cohesive-nonadhesivelayer, it is preferred to have that aluminizing layer less than about1/2 micron thick. Thus, when such a laminate has a cohesive-nonadhesivecoating on the face opposite the aluminized surface, coiling thelaminate tends to cause l(after a few weeks) some of the aluminum to belifted from the polyethylene terephthalate by the cohesive-nonadhesive.This so-called blocking tendency is much reduced where the aluminumlayer is less than 1/2 micron thick.

the blocking can also be reduced or completely eliminated by coveringthe exposed aluminum layer with a slip sheet of siliconized paper, forexample, or by applying over the aluminum an electrically conductive ornon-conductive protective coating. Such a protective electricallyconductive coating is, for example, an electrically conductive resinsuch as polyacetylene or a resin binder containing electricallyconductive fibers or finely divided particles or the like. Graphitefibers about 20 to about 50 microns long are very effective for thispurpose, particularly when they are plated with a metal such as nickel.An acrylic resin dissolved in methylethylketone, or dispersed in water,and mixed with a small amount of nickel-coated graphite fibers makes avery effective anti-blocking coating after it is applied to the aluminumand dried to form an adherent protective layer 15 to 20 microns thick.Acrylic binders such as polymethyl methacrylate are preferred for thecoating because they make harder coatings. Such electrically conductivecoatings can also be used in place of the external aluminized layer.

According to the present invention, heat sealing of backed foam wrapperscan also be effected when the foam is not thermoplastic. To this end, anopen-cell foam layer can be laminated to a support sheet of paper or thelike, using a pressure-sensitive or meltable laminant to secure the foamlayer to the support sheet. Typical pressure-sensitive laminants forthis purpose are described in application Ser. No. 768,103, filed Aug.21, 1985, now abandoned. The laminate so made will heat seal to itselffoam-to-foam when the sealing heat and pressure liquefies the laminantof one laminate and forces that laminant through the open-celled foam tocontact the foam of the laminant to which it is heat sealed. Only one ofthe laminates need have such a migrating laminant, but better resultsare obtained when both laminates have it. In the heat sealing,sufficient pressure is used not only to cause the laminant migration,but to also squeeze the cushiony foam layer to a fraction of its normalthickness, so the migrating distance is quite short, as little as 1/2 to1 millimeter.

Closed-cell foam layers do not lend themselves to the foregoingmigration sealing and should be thermoplastic so as to melt during theheat sealing, as described in application Ser. No. 913,071, filed Sep.26, 1986, now U.S. Pat. No. 4,774,800; and in parent Ser. No. 783,430,filed Oct. 4, 1985, now U.S. Pat. No. 4,693,056. Complete melting of thefoam thicknesses at the foam-to-foam heat-sealing site is preferredinasmuch as this permits the foam-backing sheets (usually paper) to beheat sealed with a melt that contains the original foam-backer laminant,and that melt provides a stronger heat seal than is provided by themelted foam alone.

Some laminants, such as those of the polyamide type and particularlylauryl lactone polymers and co-polymers, provide exceptionally strongbonding adhesion. That strength is such that it provides excellentsupport backing, as well as adhesion for the foam. Thus, where it haspreviously been considered desirable to use polyethylene terephthalatefilms at least 25 microns thick as a backing for a foam layer to make apackaging wrapper, the use of such polyamide laminant to adhere the foamto the backing makes it practical to reduce the polyethyleneterephthalate film thickness to as little as 10-12 microns and even toeliminate that backing altogether. The polyamide laminant can then bemelted and roll-coated on the face of a closed-cell foam sheet, forexample, to add about a 10 to 20 micron layer of the laminant, and theresulting material permitted to cool to provide a flexible well-backedcushiony foam sheet.

The polyamide-type laminants are particularly desirable because they arelow-melting and thus can be applied as a hot melt without injuring thefoam or whatever backing is used. Laminant melting points below about120° C. are preferred. These laminants are quite viscous when melted, sothat their application by roll coating is a slow one. They can beextruded into thin films which can be applied hot to the foam surface,or stretched to reduce film thickness and then applied and pressed intoplace by passing such foam-film combination through a nip betweenrollers. The surface of the roll in contact with the film can be heatedand made of polytetrafluoroethylene.

Laminants of the ethylene/acrylic acid co-polymer type or of thethermoplastic block rubber type also provide very high bond strength andare less viscous.

Where a supported foam layer is adhered to an object such as the outsideof a package by a pressure-sensitive coating on the foam, the subsequentpulling off of the supported foam from the object generally results insome of the foam tearing off and remaining adhered to the object. Thisis a particular problem when the foam has a low tensile strength as whenit is made of a polyolefin such as polyethylene or polypropylene, or hasa high expansion.

This problem can be avoided by laminating to the face of the foam a verythin porous sheet of high-tensile strength. Such laminating is theneffected by a coating of pressure-sensitive adhesive that is applied soit penetrates through the pores of the high-tensile sheet. In this way,an ordinary foam-paper wrapper sheet can have its foam face laminated toa 25-micron thick sheet of open spun-bonded polyethylene terephthalatefibers which has been roll-coated with or pulled through a body ofliquified pressure-sensitive adhesive. A protective top sheet ofsilicone-treated paper can then be applied over the spun-bonded sheetand the resulting sandwich subjected to the pressing action of niprollers to assure that the spun-bonded sheet is securely bonded inplace.

Alternatively, the pressure-sensitive coating can be applied directly tothe face of the foam or to the silicone-treated face of the protectivesheet, so it is squeezed into place in the nip of the rollers.

No protective sheet is needed when the wrapper is dispensed from coilsand the outer face of the foam-supporting sheet is siliconized.

The porous sheet should have a tensile strength at least three times andpreferably at least five times the tensile strength of the foam. Also,in the interest of economy the porous sheet should be not over about 50microns thick. Other high-strength fibers such as polyamide fibers ortensilized polyolefin fibers can be substituted for the polyethyleneterephthalate fibers of the porous sheet. Spun-bonded polyethylenesheets are described in U.S. Pat. No. 4,644,045.

Instead of spun-bonded sheets, the porous sheets can be screen meshhaving mesh openings no larger than about 5 millimeters, but preferablysmaller than about 3 millimeters.

The foregoing combinations with porous sheets are less expensive tomanufacture than the similar prior art combinations that use non-poroussheets instead. A single pass through a two-roll laminator will applysuch a porous sheet and also apply the laminant so it adheres the poroussheet to the foam and also covers the outer surface of the porous sheet.

Another improvement of the present invention is described in connectionwith FIG. 5 which shows a package 80 in which an electrically sensitiveobject 82, such as a circuit board is held in an envelope 84 made of alayer 86 of cushiony foam laminated to a polyethylene terephthalatesheet 88 that is metallized on both its faces. The metallizing ispreferably about the same on both faces; together they are heavy enoughto make the polyethylene terephthalate sheet quite opaque even when thatsheet is quite transparent before metallizing.

The thickness of that sheet should not be over about 25 microns, and ispreferably no thinner than about 22 microns. The two metallizing layers,generally aluminum, provide particularly effective dual shielding of thepackage contents against external electrical influences.

The cushiony foam layer can be the microcellular closed-cellpolypropylene foam described in U.S. Pat. Nos. 4,086,384 and 4,263,380,but any other cushiony foam of polyethylene, polystyrene, polyvinylchloride or polyurethane can be used. The thickness of the foam layer ispreferably from about 1 to about 7 millimeters. Only 3 millimeters orless are enough for securely packaging light-weight objects such ascomputer discs of the floppy or rigid types.

The outer face of the foam, which is the face not laminated to thepolyethylene terephthalate sheet, preferably carries sufficient antistatto keep from developing a serious static charge build-up when anythingis slid over that surface. Any of the antistat agents disclosed inparent Ser. No. 873,819, filed Jun. 13, 1986, now abandoned or in U.S.Pat. Nos. 4,321,297 and 4,584,225 can be used as long as they providethe generally desired short static discharge time--generally about 0.4second.

The envelope 84 is preferably made by folding a sheet of the laminatealong the line 90--90 and adhering the side edges 92, 92 of one fold tothe corresponding side edges of the other fold. Such adherence can beeffected by heat sealing or cold sealing, along the lines described inparent Ser. Nos. 873,819, filed Jun. 13, 1986, now abandoned and783,430, filed Aug. 21, 1985, now abandoned or by ultrasonic bonding asalso disclosed in Ser. No. 783,430, filed Aug. 21, 1985, now abandoned.Substituting ultrasonic vibrators and anvils for some or all of themelting shoes and supports in the sealing apparatus of Ser. No. 873,819,filed Jun. 13, 1986, now abandoned is particularly desirable.

The folds of the FIG. 5 envelope can alternatively be secured togetherwith ordinary cements or even by stapling. The continuity of themetallized layers from one fold to the other improves their Faraday cageeffect in electrically protecting the objects packaged. The outer edgesof the seals can be coated with sprayed-on aluminum, or conductivesilver paste or the like to also improve the electrical continuityaround those edges.

Envelope 84 also has a closure flap 94 which spans the free ends of itsfolds and thus adds further to the electrical protection. For bestprotection, that flap can be sealed against the fold it overlies, in anyof the various ways described for the side-edge sealing, including heatsealing with heated applicators, or ultrasonic heating, cold sealingwith cohesive-nonadhesive cement or pressure-sensitive cement coatingson the underside of the flap, as well as on the fold against which itlies, or even stapling.

Packaging can also be effected by using separate sheets of laminate 84sandwiched over the top and bottom of the packaged object 82, asdescribed in the parent applications. Those separate laminate sheets canbe heat sealed, cold sealed or stapled together around the packagedobject.

An electrically conductive foam can be used in place of simple foams.Very finely divided carbon, preferably acetylene black, is readilyincorporated in a melted resin like polypropylene before it is foamed,and can yield a foam having an electrical resistance of 1,000 or lessohms per square, even when the foam has an expansion as high as 10.Finely divided metals such as a low-melting tin-zinc alloy having about60% tin by weight can be used in place of or in combination with thecarbon in amounts as high as 35% of the foam. Low-melting metals likethe above alloy have melting points near or even below the meltingpoints of the resin into which they are to be incorporated, and canreadily be distributed throughout the resin by heating such liquidmixtures. Polyurethane and rubber foam can similarly be made byincorporating finely divided conductive particles in liquid resinprecursors or latexes.

With such conductive foams it is still helpful to have at least onemetallized coating on the backing for the foam, and plain paper orpolyethylene terephthalate can be used where maximum antistat protectionis not needed or the foam thickness is greater than 2 millimeters.Antistat coatings are not needed when such conductive foams are used.For cushioning purposes the conductive foam layers, like thenon-conductive foam layers, are from about 1 to about 7 millimetersthick, preferably from about 2 to about 4 millimeters thick. Either typeof foam can be open-celled or closed-celled. If little or no cushioningis needed, the conductive foam layer can be as thin as 50 microns andcan be replaced by as little as 10-micron thick layers of unfoamedconductive resin.

The highly specular nature of the outer metallized surface of thepolyethylene terephthalate laminations can be subdued by graining thatsurface preferably before it is metallized. A mild sandblasting withvery fine sharp sand is quite effective, as is the casting of thepolyethylene terephthalate sheet against a grained mold surface or therolling of that sheet between rollers, at least one of which is grained.Such graining of the polyethylene terephthalate sheet helps mask thefingerprints which are normally picked up upon handling the laminate.

The package 100 of FIG. 6 has an envelope 102 generally similar in shapeand construction to the envelope 84 of FIG. 5. Instead of thepolyethylene terephthalate backing sheet of FIG. 5, envelope 102 has aniron foil backing sheet 104. That foil is preferably a fairly pureessentially carbon-free annealed iron which has a very high magneticpermeability and a very low remanence. A one-to-three mil thick foil ofthis type provides good magnetic shielding for the contents of envelope102, such as a magnetic recording disc 106. A similar foil of iron whichcontains 1% to 3% silicon is also quite effective.

Metal foil 104 provides sufficient rigidity to stiffen the entireenvelope and also enable its flap 108 to remain in place withoutcementing. Envelope 102 can, accordingly, be used both for shipping itscontents, as well as for storing those contents between times when theyare intermittently withdrawn for use in a computer or the like. The flapis readily folded open for such withdrawal and re-insertion.

The iron foil can have its external face treated to inhibit corrosion.It can, for example, be coated with aluminum, silver or copper, whichprovide highly conductive skins that help protect against externalelectrical influences, or merely coated with a corrosion inhibitor suchas partially reduced zincdichromate. The foam layer can also carryvolatile corrosion inhibitor that helps protect the foil, particularlyits foam-contacting face.

Any metal having a magnetic permeability and remanence approximatingthose of pure iron provides effective magnetic shielding for thecontents of envelope 102.

Envelope 102 can be formed in other ways, as for example, by having itsupper fold 111 wider than its lower fold 112 and projecting beyond bothside edges of the lower fold. Those projecting margins can then befolded about the edges of the lower fold and engaged against the lowersurface of the lower fold 112. Where those folded-over margins aresufficiently stiff, they need not be adhered to the lower surface offold 112. Alternatively, they can be adhered to that lower surface as bystaples 114 as in FIG. 6 or by adhesives or by having the extendingmargins of upper fold 111 free of foam so those margins can be solderedto the lower surface of fold 112. Where staples are used as in FIG. 6,they are preferably also of pure iron so they magnetically interconnectthe foil of the folds at their edges. Adhesives or heat sealing can alsobe used and heat sealing can be arranged to melt most or all of the foamin the heat-sealing zone to thus shorten the air gap at the fold edges.The outer edges of the heat seals can be painted with a sprayed-on layerof magnetic iron to still further reduce the magnetic gap.

A flap 108 is not needed on the envelope 102 of FIG. 6, particularly ifit is only proposed to hold a thin magnetic disc.

The magnetic protection of FIG. 6 is further improved by dividing thefoil 104 into two layers that are separated by a non-magnetic gap. Thus,two layers of 0.5-to-1 mil thick iron foil coated on one face with abouta 10-micron thick layer of polyethylene or polystyrene or the like canbe laminated together with one of the thin coatings between the foilsand the resulting assembly laminated to the foam layer. The foam can becemented to the uncoated face of one of the iron foils so the outer faceof the outer foil carries the thin coating as a rust-preventative or thelike.

The anti-stat sheets, whether or not they contain foam, can be used asfloor mats or the like in so-called "clean rooms" where electronicoperations are conducted. Such sheets preferably have a surface that isat least a little resistant to slide when placed on a floor, forexample. A thin layer of cushiony foam about 1 millimeter thick providesadequate friction, as does a coating of low-tack pressure-sensitiveadhesive, or even a coating of cohesive-nonadhesive. Such coatings cancontain anti-stat as noted above and in addition anti-stat can be coatedon the opposite face of the sheet or incorporated in the sheet body. Apaper sheet is not very rugged and it is preferred to have a sheet ofspun-bonded type or of polyethylene film or other wear-resistantplastic. Such a mat placed on a floor will not permit material build-upof static electricity when walked on by people.

Anti-stat sheets, with or without foam can also be used to seal or coverpackages containing sensitive material. Thus in the package illustratedin U.S. Pat. No. 4,790,433, the cover foil can be modified so that it isbetter suited for manufacture as well as handling. To this end themetallized polyethylene terephthalate core of that foil can have a filmof polyethylene or polyethylene terephthalate adhered to its metallizedsurface, and an antistat coating over the film, with another antistatcoating on the unmetallized face of the polyethylene terephthalate core.A layer of antistat cohesive-nonadhesive can overlie the latteranti-stat to help the sheet bond to a cohesive-nonadhesive surface layeron the bottom shelf of the '433 package. Suitable antistatcohesive-nonadhesives are disclosed in published PCT application WO87/01092.

The polyethylene or polyethylene terephthalate layer over the core,protects the metallization and prevents picking of that metallizationwhen the sheet is wound up in roll form. The polyethylene layer over thecore can be as much as 62 microns thick, or as little as about 25microns thick. On the other hand the polyethylene terephthalate layerover the core is preferably from about 12 to about 25 microns thick. Thepolyethylene terephthalate core is preferably only about 24 microns,although it can be thicker particularly when the cover layer isrelatively thin. The metallization is preferably light so as to permitviewing of the packaged material right through the cover sheet.

The cover sheet can also be made easily removable so that the opening ofthe package is simplified. By way of example a tear tab can be insertedbetween the cover and the lower portion of the package so as to projectfrom the package and permit a person to lift the cover away.

The wrappers of the present invention are generally marketed as largecylindrical rolls that may be 5 or 6 feet high and be rolled up withabout 250 or more feet of wrapper. However, for some purposes, such aswrapping narrow objects, the rolls may be slit down to 12 inches or soeach slit-down roll with the 250 feet or more of wrapper. Such slit-downrolls are preferably packed in dispenser type packages for convenientuse by the customer.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

I claim:
 1. A paper sealing tape in which the paper is from about 40 toabout 90 pound weight, one face of the paper has a slip coating, and theother face carries a layer of pressure-sensitive cement in which isembedded reenforcing fibers to give the tape a breaking strength about100 or more pounds per two inch width.
 2. The combination of claim 1 inwhich the cement layer is covered by a slip sheet.